Identical twin sisters Alex and Hannah are the owners of Murder and Mayhem, a mystery bookshop that sells their famous poison-themed Killer Chocolates. But now, there's a real killer in their midst. Shortly before Christmas, their septuagenarian neighbor, Jane, confides to Alex that a murderer from a true-crime show has taken up residence in the village. The next morning, Alex shows up at Jane's house to watch the show, but instead discovers Jane's body, with a box of Killer Chocolates nearby. When Alex gets hold of Jane's journal, she begins to understand the truth.